The enclosed document describes our proposed research for the five year period commencing May 1, 1981, the continuation of a program studying biosynthesis of thyroid hormone and the action of thyroid hormone. The studies under the current grant will be directed specifically toward understanding of how occupancy of the nuclear triiodothyronine receptor is translated into a metabolic response to the hormone. We will develop new methods for purifying receptor by affinity chromatography. We will study the physiology of uptake of the receptor by the nucleus and the mechanism of the binding of the receptor to chromatin. We will study binding of the receptor to nucleosomes and to DNAse prepared fragments of chromatin and study the role of specific nonhistone proteins in binding of receptor to chromatin. The mechanisms affecting the release of receptor from nuclei will also be investigated. We will study the metabolic function of thyroid hormone analogs which are able to bind to the receptor, to determine whether they function as agonists, partial agonists, or antagonists. We will study responses to thyroid hormone, looking for the earliest evident response. We will especially be interested in studying the action of phosphokinases in cytosol and liver cell nuclei, and attempt to identify quantitative and qualitative changes in phosphokinase function as well as possible translocation of phosphokinase, and the specific proteins phosphorylated. We will attempt to reconstitute an in vitro system in which the effect of the receptor-T3 complex can be shown (possibly) to stimulate the formation of mRNA directly in vivo by an action on nuclei, polymerase, or chromatin. We will study the triiodothyronine binding capacity of human circulating lymphocytes in a variety of abnormal conditions which are known to alter receptor function in animals.